# NTSB FTW98LA253: Hiller UH-12E, N4028T, Delaplaine, AR, June 2, 1998 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 2, 1998, 18:15 local (23:15 UTC) - Place: Delaplaine, AR - Coordinates: 36.229171, -90.719627 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.2292&lon=-90.7196&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report December 1, 1999 - Report: Approved by Office Director - ADs cited in the narratives: [AD 81-17-03](https://openairdocs.org/ad/81-17-03) (OpenAirDocs) - NTSB case key (mKey): 20636 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW98LA253 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/20636/pdf - Page: https://openairdocs.org/ntsb/FTW98LA253 ## Probable cause The failure of maintenance personnel to comply with and airworthiness directive, which resulted in failure of the planetary gear due to lack of lubrication. A contributing factors was the lack of suitable terrain for the pilot to execute a forced landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, maneuvering - aerial application - lubricating system,oil filter/screen - flow restricted (cause) - maintenance,compliance with ad - not performed, company maintenance personnel (contributing factor) - rotor drive system,main gearbox/transmission - failure,total (cause) - Forced landing, descent - emergency - autorotation - initiated, pilot in command - On ground/water encounter with terrain/water, emergency landing - terrain condition - none suitable (contributing factor) ## Analysis The helicopter was traveling in an easterly direction at an airspeed of 60 knots, while maintaining a constant 5 foot clearance over the rice field, when the transmission failed. The pilot turned the helicopter to the right to avoid a tall tree, as he simultaneously initiated a forced landing. During the touchdown on soft ground, both skids and the collapsed and the tailboom was severed by the main rotor blades. According to the maintenance records, the main transmission (part number 23700-9, serial number 617), which has a recommended TBO of 1,200 hours, had accumulated 1,048 hours since its last overhaul in 1993. According to the manufacturer, the 23700-9 transmissions are subject to a recurring inspection of the oil filter every 50 flight hours in accordance with Airworthiness Directive 81-17-03. According to the maintenance logbooks, the last compliance with AD 81-17-03 was 340 hours prior to the accident, on March 26, 1996. Examination of the transmission by the manufacturer's representative revealed a massive failure of the first stage planetary gear system due to lack of lubrication. ## Factual narrative On June 2, 1998, at 1815 central daylight time, a Hiller UH-12E helicopter, was substantially damaged during a forced landing following a main transmission failure while maneuvering near Delaplaine, Arkansas. The commercial pilot, sole occupant of the helicopter, was not injured. The helicopter was owned and operated by Wilson Flying Service, Inc., of Walnut Ridge, Arkansas. Visual meteorological conditions prevailed for the local Title 14 CFR Part 137 aerial application flight for which a flight plan was not filed. The flight originated from a nearby farm approximately 5 minutes prior to the accident. The pilot reported that he was in the process of completing his sixth aerial application pass while dispensing herbicides on rice fields using east to west spray swaths. The helicopter was traveling in an easterly direction at an airspeed of 60 knots, while maintaining a constant 5 foot clearance over the rice field when the failure occurred. The pilot further stated that the helicopter was operating normally until he heard a loud grinding and growling noises coming from the area of the main transmission. The grinding noise, which was accompanied by a severe vibration, was proceeded by "the needles splitting and a marked increased in engine RPM." Suspecting an imminent transmission failure, the pilot turned the helicopter to the right to avoid a 50 foot tall cottonwood tree, as he simultaneously initiated a forced landing to an area short of a ditch and a tree line. During the touchdown in the soft ground, the left landing gear skid broke, the main rotor blades impacted the ground and the tailboom was severed by the rotating rotor blades. The helicopter came to rest in the upright position on a heading of 240 degrees, with both skids and crosstubes collapsed. Maintenance records that were provided by the operator, were reviewed by a FAA inspector. Entries in the records indicate that the main transmission (part number 23700-9, serial number 617), which has a recommended TBO of 1,200 hours, had accumulated 1,048 hours since its last overhaul in 1993. According to the manufacturer, the 23700-9 transmissions are subject to a recurring inspection of the oil filter every 50 flight hours in accordance with Airworthiness Directive (AD) 81-17-03. According to the maintenance logbooks, the last inspection in accordance with AD 81-17-03 was completed 340 hours prior to the accident, on March 26, 1996, at 708 Hobbs hours (1,908 hours total airframe hours). Examination of the transmission by a manufacturer's representative revealed "a massive failure of the first stage planetary gear system due to lack of lubrication." See enclosed manufacturer's report dated June 17, 1998, for details of the examination. ## Aircraft - Registration: [N4028T](https://openairdocs.org/deregistered/N4028T-1999-06-10), registration cancelled 1999-06-10, S/N 5097 (OpenAirDocs) - Reported make and model: Hiller UH-12E - Registry model: [Hiller UH-12E](https://openairdocs.org/model/hiller-uh-12e) (registry code 4360122) (OpenAirDocs) - Category: Helicopter - Serial number: 5097 - Airframe hours: 2961 - Engines: Lycoming VO-540-C2A 340 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Registered owner: Frank And Judy Wilson - Airworthiness certificate: Standard, Normal; Special, Restricted (Special) - Last inspection: 100 hour, May 24, 1998, 25 hours before ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 55; commercial; airplane ratings: single-engine land, multi-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: center; flight hours: 22,000 total, 8,000 in this make and model, 20,000 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 210° at 13 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 97 °F, dew point 66 °F - Altimeter: 29.00 inHg - Observed at: ARG, 12 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19980602012139A](https://openairdocs.org/incident/19980602012139A), Jun 2, 1998: Hiller UH12E, Deleaplaine, AR, Substantial damage. Acft experienced engine problems, pilot made emerg landing in the field, broke the skid, main rotor struck the grou (.4)the helicopter was traveling in an… ## Other investigations on N4028T (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB CHI89DEM09](https://openairdocs.org/ntsb/CHI89DEM09), Sep 28, 1989: Hiller UH-12E (N4028T), Hudsonville, MI, substantial damage. Probable cause: THE FATIGUE FAILURE OF ONE OF THE TENSION-TORSION PINS. From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.